The layered transition-metal dichalcogenides have applications in areas as diverse as lubrication, electrochemistry, and catalysis. For example, the lubricity of the layered compound molybdenum disulfide, MoS2, stems from the weak bonding between adjacent basal planes. Molybdenum disulfide is a known catalyst for conversion of syngas to hydrocarbons plus carbon dioxide and water. When certain alkali salts (base promoters) are added, the catalyst selectivity is altered to direct syngas toward alcohols. Under appropriate conditions, the product alcohols comprise primarily methanol and ethanol. The base promoter can be an anionic, cationic, or molecular species. A typical base promoter is an alkali metal, such as potassium. The deposition process is usually intended to disperse the promoter broadly and uniformly. However, good distribution of base promoters can be difficult.
Components, such as base promoters, can be introduced into transition-metal dichalcogenides (such as MoS2) in a number of ways. It is known that cations or neutral molecules can be inserted between MoS2 sheets (Whittingham, Prog. Solid St. Chem., 12, 41-99, 1978).
For example, lithium can be introduced or “intercalated” by soaking the layered compound in a solution of n-butyllithium in hexane, as described by M. B. Dines in U.S. Pat. No. 3,933,688, issued in 1976. Other prior methods of obtaining a layered compound with alkali metal between the layers are, for example, intercalation of the transition metal dichalcogenide with the alkali metal from solution in liquid ammonia as described by W. Rudorff in Chimia, Vol. 19 (1965); or by electrointercalation in an electrochemical cell as described by R. R. Haering et al. in U.S. Pat. No. 4,224,390, issued in 1980; or by exposing the layered compound to hot alkali metal vapors as described in Intercalated Layered Materials, edited by F. Levy (1979).
Another method starts from MoS2 containing intercalated Li+. In water, the Li—MoS2 can exfoliate into detached sheets. These sheets will spontaneously restack when the solvent is removed, but with molecules or cations trapped between the layers (Yang and Frindt, J. Phys. Chem. Solids, 57, 1113-1116 (1996); Heising and Kanatzidis, J. Am. Chem. Soc., 121, 11720-11732 (1999)).
U.S. Pat. Nos. 4,822,590 and 5,072,886, to Morrison et al., disclose how layered or porous materials intercalated with alkali metals may be fractured into higher-surface-area materials by immersing the intercalated material in a liquid that generates a gas upon reaction with the alkali metal. It is suggested that the fractured materials may be useful in catalysis.
The aforementioned methods of intercalating transition-metal dichalcogenides can be impractical or costly. In light of the shortcomings in the art, what is desired is an intercalation approach that can be more efficient and/or more practical. When alcohols are desired from syngas, via base-promoted catalysis, it would be especially convenient to add a base promoter by dry-mixing the promoter and catalyst precursor solids. Suitable in situ or ex situ conditions for intercalation of the base promote are needed, wherein the promoter migrates as it is melted, volatilized, or otherwise rendered mobile.